combustible
The foam cools and sets, giving a light, strong, incombustible wall.
Water is sprayed into the container, wetting the contents and making them incombustible.
The result is an incombustible material with an extraordinary compressive strength.
Some cities collect plastics as combustible waste, whereas others collect them as incombustible refuse.

SMART Vocabulary: related words and phrases

Burning, burnt & on fire
afire
aflame
alight
blaze
burn (something) down
burn sb up
burned out
burnt out
char
consume
flare
frazzled
inflammable
post-burn
reignite
scald
scorch
self-immolation
unburnable
unburned